Metastatic cutaneous plasmacytoma: a case report associated with IgA lambda multiple myeloma and a review of the literature of metastatic cutaneous plasmacytomas associated with multiple myeloma and primary cutaneous plasmacytomas.

We present the case of a 67-year-old Japanese woman with immunoglobulin A lambda (IgA lambda) multiple myeloma (MM). She had firm nodular cutaneous lesions on the trunk and scalp without adjacent bone involvement. The patient was diagnosed as having IgA lambda MM of stage IIIA with 52% plasmacytosis in the bone marrow six months before the appearance of the cutaneous lesions. The abnormal plasma cells showed moderate to marked dysplasia in both the bone marrow and skin lesions. The abnormal plasma cells in the bone marrow exhibited abnormal karyotypes: 41, XX, der (1) t (1p; 1q), -4, -10, -14, -16, -17, 17p+, that differed from the "unfavorable" karyotype reported previously. We reviewed the cases of metastatic cutaneous plasmacytoma in MM and cases of primary cutaneous plasmacytoma that have been reported in English or Japanese and identified the Ig class. Among the 83 cases of metastatic cutaneous plasmacytomas in MM, IgG, IgA, IgD, and Bence-Jones protein were found in 52%, 23%, 16%, and 6%, respectively. A disproportionately high frequency of IgD lambda MM was found to have spread to the skin, compared with the frequency of IgD MM itself, which was present in only around 2% of the MM cases. Among the 18 primary cutaneous plasmacytomas, IgG, IgA, and Bence-Jones protein were found in 56%, 11%, and 17%, respectively, but no IgD was found.